As well known, a seat unit can be mounted on many children products such as strollers, the chasses of the car seats, etc. However, the connection of a seat unit and a children product generally necessitates the employment of a connecting means, which in most cases is complicated and can only be practicable with the assistance of extra components. Using of extra components leads to at least one significant disadvantage, that is, the operator can be easily confused and feel hard to operate. Another disadvantage lies in that, once the seat unit is separated from the child stroller, one has to remove the extra components away when using the child stroller, which will cause great trouble.